1. Field of the Invention
The present invention relates to a packet multiplexing apparatus and a method of forming a packet in a packet multiplexing apparatus.
2. Description of the Related Art
In a conventional example of a packet multiplexing apparatus, when a digital video and audio data of high quality, a high transmission rate general-purpose data, and a plurality of low transmission rate general-purpose data are multiplexed in a packet having a fixed length, the TS multiplexing (transport stream multiplexing) of the MPEG2 system is adopted. The general purpose data may include a video data and a speech data in addition to character data and so on.
FIG. 1 shows the payload and the TS packets. Referring to FIG. 1, the low transmission rate general-purpose data is converted into packets and is put on a payload section of each of private PES packets which can be freely used by a user. The data is divided and put on the TS packets. Each of the TS packets has the fixed length and is added with an identifier which indicates that the packet is the privacy PES packet. Then, the TS packets are transmitted onto a network.
Thus, in the conventional example of the packet multiplexing apparatus, each of the general-purpose data is divided into the payload section of the packets which has the identifier corresponding to the general-purpose data and then transmitted onto the network.
Also, because the above digital video and audio data have a high transmission rate, it is important that the video and audio data are transmitted at real time. In this case, the packet length of the above TS packet is set to be comparatively long.
In the above-mentioned conventional example of the packet multiplexing apparatus, when the above low transmission rate general-purpose data to be converted into packets, a long time is required until the data for the payload length of the TS packet is stored in a memory. As a result, the delay between communication ends is large. For instance, in the TS multiplexing in the MPEG2 system, when the low transmission rate data of 1200 bits/sec is put on the payload section of 184 bytes without any stuffing, as shown in FIG. 2A, about 1.2 seconds is required to convert into the packets. On the other hand, if a stuffing area is provided for the payload section of the fixed length packet to reduce this delay, as shown in FIG. 2B, the transmission efficiency is decreased by the stuffing area.
A TDM-packet converting circuit is described in Japanese Laid Open Patent Application (JP-A-Heisei 3-106149). In this reference, there are provided a 2-plane buffer having a storage area for each of channel numbers and a TDM control section which holds a channel number data and channel rate data corresponding to each of channels on a TDM bus. A write control section performs plane switching of the buffer on a write side in a switching rate in accordance with the channel rate and writes a data on the TDM bus in a corresponding area of the switched buffer in accordance with the channel number data. A packet control section holds a relation data between a frame address on a packet reception side and the channel number. A read control section performs a plane switching of the buffer on a read side in accordance with the channel rate and reads a data by a predetermined amount from the corresponding area of the buffer in accordance with the channel number.
Also, a time divisional multiplexing data packet converting circuit is described in Japanese Laid Open Patent Application (JP-A-Heisei 3-109841). In this reference, the time divisional multiplexing data packet converting circuit is composed of a time divisional multiplexing data/packet converting section for reading by a predetermined amount a time divisional data which is written in a first data storage means for every channel in accordance with information indicative of a relation between each of time slots and a channel number to form a packet, and a packet/time divisional data converting section for reading a data of an inputted packet by a predetermined amount which is written in a second data storage means for every channel to form the time divisional multiplexing data in accordance with the relation between each of time slots and a channel number. In this case, a first channel rewriting means rewrites channel numbers having the same destination and the same rate, which are written in a first data storage means, into a same channel number. A second channel number rewriting means rewrites the same channel number which is read out from a second data storage means into an original channel number.
Also, a speech packet communication apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 4-348636). In this reference, a speech present state of each of channels from a PBX is detected by a CODEC section. A block discard control section has a traffic calculating function and a discard function. In the traffic calculating function, a transmission amount which is allowed to be transmitted to a time divisional multiplexing unit is calculated based on the number of channels of the speech present state. Also, in the discard function, the determination of discarding and execution of the discarding are performed in accordance with a discarding algorithm defined based on the traffic calculating result. Thus, accumulation of data in a transmission buffer is prevent. As a result, the increase of delay time is prevented.
Also, a packet sending system is described in Japanese Laid Open Patent Application (JP-A-Heisei 7-226773). In this reference, a priority flag checking section checks whether or not a priority flag is present in a secondary header of a packet from a buffer and outputs the checking result. A release timing generating section generates a release timing signal when time-out is detected based on a reference time signal from a time generating section or when a priority flag detection signal is inputted. A multiplexing section multiplexes packets inputted from the buffer via the priority flag checking section. Also, the multiplexing section adds a header having a fixed length to form a frame of a fixed length. The multiplexing section forms a frame of the fixed length in which a fill packet is filled in an empty area of a data field, immediately when the release timing signal is inputted during the multiplexing. Thus, the delay time of a critical packet is shortened.
The present invention is accomplished to solve the above problems. Therefore, an object of the present invention is to provide a packet multiplexing apparatus in which increase of multiplexing delay can be suppressed without degradation of a transmission efficiency.
Another object of the present invention is to provide a method of multiplexing packets.
In order to achieve an aspect of the present invention, a packet multiplexing apparatus includes at least one high transmission rate data memory for accumulating high transmission rate data, and at least one low transmission rate data memory for accumulating low transmission rate data. A control section determines whether an accumulation quantity of the high transmission rate data reaches a first predetermined value, and issues a transmission instruction when it is determined that the accumulation quantity of the high transmission rate data reaches the first predetermined value. A multiplexing unit multiplexes the high transmission rate data from the high transmission rate data memory and the low transmission rate data from the low transmission rate data memory in response to the transmission instruction to form a packet.
In this case, the packet multiplexing apparatus may further include an inputting unit for inputting the first predetermined value to the control section.
The control section may determine whether an accumulation quantity of the low transmission rate data reaches a second predetermined value, and may issue the transmission instruction when it is determined that the accumulation quantity of the low transmission rate data reaches the second predetermined value. In this case, the packet multiplexing apparatus may further include an inputting unit for inputting the first and second predetermined values to the control section.
The packet is a packet of a fixed data length.
In order to achieve another aspect of a packet multiplexing apparatus include at least one high transmission rate data memory for accumulating high transmission rate data, and at least one low transmission rate data memory for accumulating low transmission rate data. The control section determines whether a ratio of an accumulation quantity of the high transmission rate data and an accumulation quantity of the low transmission rate data reaches a predetermined value, and issues a transmission instruction when it is determined that the ratio reaches the predetermined value. A multiplexing unit multiplexes the high transmission rate data from the high transmission rate data memory and the low transmission rate data from the low transmission rate data memory in response to the transmission instruction to form a packet.
In this case, the packet may be a packet of a fixed data length, and the packet multiplexing apparatus may further include an inputting unit for inputting the predetermined value to the control section.
In order to achieve still another aspect of the present invention, a method of forming a packet in a packet multiplexing apparatus, includes the steps of:
accumulating high transmission rate data in a high transmission rate data memory;
accumulating low transmission rate data in a low transmission rate data memory;
issuing a transmission instruction based on an accumulation quantity of the high transmission rate data and an accumulation quantity of the low transmission rate data; and
multiplexing the high transmission rate data from the high transmission rate data memory and the low transmission rate data from the low transmission rate data memory in response to the transmission instruction to form a packet.
In this case, the issuing step may include determining whether the accumulation quantity of the high transmission rate data reaches a first predetermined value, and issuing the transmission instruction when it is determined that the accumulation quantity of the high transmission rate data reaches the first predetermined value. In this case, the first predetermined value is desirably inputted by a user.
Instead, the issuing step may include determining whether the accumulation quantity of the low transmission rate data reaches a second predetermined value, and issuing the transmission instruction when it is determined that the accumulation quantity of the low transmission rate data reaches the second predetermined value. In this case, the second predetermined value is desirably inputted by a user.
Alternatively, the issuing step may include determining whether a ratio of an accumulation quantity of the high transmission rate data and an accumulation quantity of the low transmission rate data reaches a third predetermined value, and issuing a transmission instruction when it is determined that the ratio reaches the third predetermined value. In this case, the third predetermined value is desirably inputted by a user.